1 /* Copyright 2006-2008 Joaquin M Lopez Munoz. 2 * Distributed under the Boost Software License, Version 1.0. 3 * (See accompanying file LICENSE_1_0.txt or copy at 4 * http://www.boost.org/LICENSE_1_0.txt) 5 * 6 * See http://www.boost.org/libs/flyweight for library home page. 7 */ 8 9 #ifndef BOOST_FLYWEIGHT_DETAIL_VALUE_TAG_HPP 10 #define BOOST_FLYWEIGHT_DETAIL_VALUE_TAG_HPP 11 12 #if defined(_MSC_VER) 13 #pragma once 14 #endif 15 16 #include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */ 17 #include <boost/parameter/parameters.hpp> 18 #include <boost/type_traits/is_base_and_derived.hpp> 19 20 namespace boost{ 21 22 namespace flyweights{ 23 24 namespace detail{ 25 26 /* Three ways to indicate that a given class T is a value policy: 27 * 1. Make it derived from value_marker. 28 * 2. Specialize is_value to evaluate to boost::mpl::true_. 29 * 3. Pass it as value<T> when defining a flyweight type. 30 * 31 * For the time being the interface of value policies is not public. 32 */ 33 34 struct value_marker{}; 35 36 template<typename T> 37 struct is_value:is_base_and_derived<value_marker,T> 38 {}; 39 40 template<typename T=parameter::void_> 41 struct value:parameter::template_keyword<value<>,T> 42 {}; 43 44 } /* namespace flyweights::detail */ 45 46 } /* namespace flyweights */ 47 48 } /* namespace boost */ 49 50 #endif 51